Catalyst-free aziridination and unexpected homologation of aziridines from imines

Article abstract of DOI:10.1039/c001894e

Aziridination and unpredicted homologation reaction of N-sulfonylimines were achieved easily with a very simple, rapid and mild procedure through the use of diazomethane without the presence of any catalyst. The method represents an attractive alternative

Full text of DOI:10.1039/c001894e

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Catalyst-free aziridination and unexpected homologation of aziridines
from imines†
Paula Se´rio Branco,* Vivek Prabhakar Raje,* Jorge Dourado and Joana Gordo
Received 28th January 2010, Accepted 16th April 2010
First published as an Advance Article on the web 11th May 2010
DOI: 10.1039/c001894e
Aziridination and unpredicted homologation reaction of N-sulfonylimines were achieved easily with a
very simple, rapid and mild procedure through the use of diazomethane without the presence of any
catalyst. The method represents an attractive alternative to metal-catalyzed processes.
Table 1 Aziridination and homologation reaction of N-tosylimines
Introduction
The use of aziridines in modern synthetic chemistry is unavoidable
due to their value as useful substrates for the preparation of
important biologically active substances, and also due to their
versatility as chiral reagents and chiral auxiliaries, precious in
stereoselective synthesis.1 Great efforts and progress have been
made in the development of various aziridination methods;2,3
however, the simplest approach is either the addition of a nitrene
moiety to an olefin or the addition of a carbene moiety to
an imine. Transition metals have been found to act as effective
catalysts in both cases, although the metal-mediated nitrene
transfer to olefins4 has been examined in much more detail than
the reaction of a metal-carbene with an imine.5 The reaction of a
variety of imines with diazocompounds is limited to substituted
diazomethanes in the presence of catalytic amounts of catalyst.6
Metal-free catalyzed processes are interesting alternatives since
they are often more economical and environmentally friendly. It is
known that the addition of diazomethane to various Schiff bases
forms 1,2,3-triazolines, and all the attempts to obtain aziridines
by pyrolysis or photolysis of the above triazolines have failed.7
To our surprise, reports on the reactions of diazomethane with
imines to produce aziridines are scarce in literature and limited to
fluorine-substituted imines,8 1-phosphono-2-aza-1,3-dienes9 and
iminium salts.10 As part of our general interest in the area of
small-ring synthesis, we have been investigating new methods to
prepare aziridines.11 We report herein our preliminary results of a
mild procedure, very simple and rapid method for the preparation
of N-sulfonyl-2-substituted aziridines, by aziridination and/or
homologation–aziridination reaction of N-sulfonylimines using
diazomethane as the carbene source. The method represents an
attractive alternative to metal-catalyzed processes, notably because
of its lower cost. Also has the advantage of being a new method for
the synthesis of 2-benzylaziridines which complement the existing
methods.
Entry
R
R¢ Time/min 2 h (%) 3 h (%)
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
Ph
Ph
Ph
Ts 30
Bs 30
Ms 20
Ts 30
Bs 30
Bs 30
Ts 30
Ts 30
Bs 30
Ts 30
Ts 30
Bs 30
Nz 25
Ts 30
Ts 10
Bs 30
Ts 30
Ts 40
71
70
70a
75
71
45
78
72
67
74
0
0
0
0
10
0
0
0
0
0
0
0
0
0
4-BrC6H4
4-BrC6H4
3-ClC6H4
4-ClC6H4
2-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
2,4-(MeO)2C6H3
2-MeC6H4
2-MeC6H4
Furanyl
Ph–CH CH
3,4-Methylenedioxyphenyl Ts 30
3,4-Methylenedioxyphenyl Bs 30
0
0
72
68
78
74
65
73
77
68
76
72
65
50
b
0
0
0
0
0
30
=
s
t
u
v
Anthracene
2-Br-4,5-(methylenedioxy)- Ts 20
phenyl
Ts 20
x
Ph
Ph 120
0
0
a Yield of crude product; any attempts to purify the product failed. The
1H NMR of crude shows aziridine peaks, compared with the reported 1H
NMR. b The reaction was quenched after 10 min.
Results and discussion
We began our investigation with a model aziridination reaction
between N-benzylidene-4-methylbenzenesulfonamide (1a) and di-
azomethane. As illustrated in Table 1, treatment of 1 equiv. of 1a
with 5 (approximately) equivalents of diazomethane in THF at -5
to 0 ◦C gave the desired aziridine, 2a, in 71% yield.
When electron-withdrawing aromatic substituents groups are
present, the reaction gave good yields of aziridine 2 (Table 1,
entry a–j). However, in the presence of electron-donating groups
(Table 1, entry k–v), the reaction products show a slightly different
1H NMR pattern, indicating two extra protons, one extra carbon
in 13C NMR and more 14 a.m.u. on the mass spectra. To this
Chemistry Department, REQUIMTE, Faculdade de Cieˆncias e Tecnologia,
Universidade Nova de Lisboa, 2829-516 Caparica, Portugal. E-mail:
psb@dq.fct.unl.pt, vivek_raje@yahoo.com; Fax: +351 21 2948550;
Tel: +351 21 2948300
† Electronic supplementary information (ESI) available: General meth-
ods, NMR spectra, and mass spectra of all compounds. See DOI:
10.1039/c001894e
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Scheme 1 The proposed mechanism for the homologation–aziridination reaction of N-tosylimines.
compound was then attributed the structure 3, which agrees with
the incorporation of two methylene groups starting from the
imine. The complete structural elucidation of 3 was accomplished
using two-dimensional NMR spectroscopy. Moreover, our spec-
troscopic data are in consonance with those presented for two re-
lated compounds reported in literature,12 N-tosyl-benzylaziridine
and N-(4-methoxybenzenesulfonyl)benzylaziridine. The results,
summarized in Table 1, show that the carbene insertion into
the imine double bond13 with concomitant formation of the
aziridine ring is limited to N-sulfonylimines 1 (entry a–v). In
fact, no reaction is observed with N-benzylidene aniline (entry
x). N-Benzenesulfonyl imines or N-tosylimines participate with
a similar degree of efficiency (entry a vs. b or k vs. l, among
others). Spectroscopic data obtained for compound 2 agree with
those already published in literature14 and also those from the
imine substrates 1 used.15 To study the reaction mechanism, the
reaction of 2-methylphenyl-N-tosylimine with diazomethane was
quenched after 10 min (entry o). Both aziridines 2o and 3o
were isolated from the reaction medium. Initially, this result lead
us to propose a reaction mechanism involving a ring opening
reaction of the aziridine primarily formed, which occurs due to
the electron-donating property of the ring substituent (Scheme 1,
route a).
In an attempt to prepare 2-phenyl-N-tosylethanimine (4,
X = H) using the routine procedure,13 the tautomeric form 5
was formed since, in the in situ reaction with diazomethane,
the methylated compound N-methyl-N-(2-phenylethenyl)-p-
toluenesulfonamide16 was the only product obtained. Hence,
to prepare 2-phenyl-N-tosylethanimine (4, X = H) a different
procedure3,17 was then followed which involved the reaction of
phenylacetaldehyde and N-sulfinylsulfonamides. Any attempt to
isolate 4 was fruitless and, therefore, the aziridination of 4 with
diazomethane was accomplished in situ and the aziridine 3a was
obtained in 50% yield.
It should be reported that the net rearrangement of aziridines
to imines has been reported under thermal conditions18 or under
Lewis acid catalysis.19 Indeed the aza-pinacol rearrangement of 2a
to 3a using BF3 was observed. After total consumption of 2a, the
reaction mixture was neutralized with solid sodium bicarbonate,
and diazomethane was added to the reaction medium. Compound
3a was obtained in low yield, 33% (Table 2-via a, entry e) which can
be explained by the fact that, in these conditions, some hydrolysis
of the imine intermediate 4 can occur. Roughly the same result
was obtained in situ starting from imine 1a. In these case, without
isolation of the aziridine 2a the aza-pinacol rearrangement was
accomplished with BF3 (Table 2-via b, entry a).
The ring opening product can subsequently undergo an aza-
pinacol rearrangement to the N-tosylimine 4 or a proton
capture and re-aromatization to 5 followed by enamine–imine
tautomerism to 4. Both the cases result in homologation of
the initial N-tosylimine by a methylene group. The proposed
reaction mechanism is outlined in Scheme 1, route a. Any
attempt to trap this N-tosylimine intermediate 4 by a Diels–Alder
reaction with 2,3-dimethylbutadiene or 2,3-diphenylbutadiene was
unsuccessful.
As expected, a substituent unable of stabilizing intermediate
6 would not favour the imine homologation via aza-pinacol
rearrangement (Table 2 entry c and f).
If compound 5 was involved as an intermediate in the reaction
(the tautomeric conversion to 4 was not expected to be so fast
since 5 is more stable due to conjugation) other type of products
would result from its reaction with diazomethane.
To further strengthen the reaction mechanism, we tried the
homologation of 2o to 3o under the same reaction conditions. But
unexpectedly, the conversion of 2o to 3o was not observed, creating
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Scheme 2 Schematic representation of the synthesis of N-(p-toluenesulfonyl)-2-(4-methoxybenzyl)aziridine (3k) from tyrosine.
Table 2 Aza pinacol rearrangement of aziridines
homologated imine 4 is an intermediate. To support the mecha-
nism, imine 1v (Table 1), N-(3,4-methylenedioxy-benzylidene)-4-
methylbenzenesulfonamide, having a bulky group on the ortho
position, was prepared and subjected to the reaction. Aziridines
2v and 3v were obtained in 30 and 50% yield, respectively. As
expected, the rate of the reaction to aziridine 3v, became slower
than that of 3s, due to the presence of bromine. These results led
us to conclude that the steric hindrance of the bromine could have
an affect on the cyclization forming the intermediate 7 (Scheme 1).
In parallel, the synthesis of compound 3k was accomplished by
a different procedure starting from tyrosine and the structure was
confirmed (Scheme 2). The synthesis started with the amino group
protection with Boc followed by methylation of the carboxylic
acid with diazomethane. Methylation of the hydroxylic aromatic
group was subsequently achieved using K2CO3/(MeO)2SO2. After
Boc removal,21 the reduction with LiAlH4 lead to the 1,2-amino
alcohol. The final step of cyclization to the aziridine ring was
carried out by tosyl chloride and potassium carbonate22 and
compound 3k was obtained in 30% overall yield.
Entry
Substrate
R
R¢
3 h (%)
a
b
c
d
e
f
1a
1e
1i
1f
2a
2i
Ph
Ts
Bs
Bs
Bs
Ts
Bs
38
25
4-BrC6H4-
4-NO2C6H4-
3-ClC6H4-
Ph
—
18.3a
33
4-NO2C6H4-
—
a 50 ml of H2SO4 was used as catalyst instead of BF3.
doubt in the mechanism involving the aza-pinacol rearrangement.
To get further insight on the reaction mechanism, we have per-
formed an experiment involving the quenching of a definite part of
the reaction mixture in scheduled times of 1/4/8/15/20/30 min.
The solvent and the rest of diazomethane were evaporated and the
crude sample was analyzed by 1H NMR. To our surprise, the imine
1o was consumed immediately, the amount of aziridine 2o was
constant throughout the reaction, and the amount of 3o increased.
The ratio of 2o to 3o increased from 1 : 1 to 1 : 3. The quantification
was done by 1H NMR using two sets of signals from the aromatic
and the aliphatic part. The signals used for quantification were the
pair of doublets at 7.58 (ArH2¢+6¢ from 3o) and 7.82 (ArH2¢+6¢ from
2o) and the double doublet at 3.80–3.77 (H2 from 2o), the multiplet
at 2.90–2.84 (H3 from 3o and H2 from 2o) and the double doublet at
2.75 (H1¢a from 3o). In light of the above observations, a mechanism
involving aza-pinacol rearrangement is not plausible. To justify
our results, a different mechanism involving intermediate 7 is
proposed (Scheme 1, route b). This mechanism is supported by a
report on the reaction of quinazolinium salts with diazomethane.20
Therein, they propose the attack of diazomethane on the polarized
double bond and a subsequent ring closure. The cycloaddition of
diazomethane to the imine double bond forming a triazole is dis-
carded because it cannot justify the lack of reaction with substrate
1x (Table 1). In Scheme 1, in both cases (route a or b), the proposed
Conclusions
In summary, we have demonstrated that the aziridination or
homologation–aziridination reaction of N-sulfonylimines are
achieved easily with a very simple, rapid and mild proce-
dure by using diazomethane without any catalyst. The method
uses readily available reagents and occurs under experimentally
straightforward conditions. The recently reported work23 on the
instantaneous deprotection of N-tosylaziridines will enlarge the
scope of its application. The method represents an attractive
alternative to metal-catalyzed processes, notably because of its
lower cost. To the best for our knowledge, this is the first time that
in situ homologation of imines is reported. Additional studies
with other diazocompounds, such as phenyldiazomethane or
trimethylsilyldiazomethane, are currently underway.
Experimental
General experimental
All commercial reagents were used as received unless
otherwise mentioned. For analytical and preparative thin-layer
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chromatography, Merck, 0.2 mm and 0.5 mm Kieselgel GF 254
precoated were used, respectively. The spots were visualized using
UV light and a DNP solution followed by heating. Medium
performance liquid chromatography and flash column chromatog-
raphy were performed using Merck, Kieselgel 60 with (0.063–
0.200 mm) and (0.040–0.063 mm), respectively. Infrared spectra
were recorded on a Perkin Elmer spectrum 1000. 1H and 13C NMR
spectra were recorded on a Bruker ARX 400 spectrometer at 400
36.5 (C1¢), 32.7 (C3), 21.5 (ArCH3). MSEI(+) m/z: 317 [M]+ (14.6),
162 [M-Ts)]+ (98.5), 121 [MeOC6H4CH2]+ (100). HRMSEI(+)
calcd for C17H19NO3S [M]+ 317.10856 found 317.1081.
N-(Benzenesulfonyl)-2-(4-methoxybenzyl)aziridine (3l). Oil,
=
obtained in 68% yield. IR(film) nmax
:
1321 (S O), 1162
(S O) cm . 1H NMR (CDCl3) d: 7.81 (2H, d, J = 7.7 Hz,
ArH2¢+6¢), 7.58 (1H, t, J = 7.4 Hz, ArH4¢), 7,44 (2H, t, J = 7,7 Hz,
ArH3¢+5¢), 6.95 (2H, d, J = 8.4 Hz, ArH2+6), 6.68 (2H, d, J =
8.4 Hz, ArH3+5), 3.77 (3H, s, OCH3), 2.99-2.93 (1H, m, H2), 2.77
(1H, dd, J=14.7 and 5 Hz, H1¢a), 2.72 (1H, d, J = 6.9 Hz, H3a),
2.62 (1H, dd, J=14.5 and 7.2 Hz, H1¢b), 2.16 (1H, d, J = 4.4 Hz,
H3b). 13C NMR (CDCl3) d: 158.3 (ArC4), 138.0 (ArC1¢), 133.3
(ArC4¢), 129.6 (ArC2+6), 128.9 (ArC3¢+5¢+ ArC1), 127.8 (ArC2¢+6¢),
113.8 (ArC3+5), 55.2 (OCH3), 41.6 (C2), 36.5 (C1¢), 32.8 (C3).
MSEI(+) m/z: 303 [M]+ (11), 162 [M-Bs]+ (96.5), 160 [M - Bs -
H2]+ (100). HRMSEI(+) calcd for C16H17NO3S [M]+ 303.0929
found 303.0924.
-1
=
1
and 100.62 MHz, respectively. H shifts are reported relative to
internal TMS. Carbon shifts are given relative to the 13C signal of
CDCl3 (d 77.0 ppm) as reference. Mass spectra were recorded
at the Mass Spectrometry Unit at the University of Santiago
de Compostela, Spain. The electron impact mass spectra were
recorded using a magnetic Micromass Autospec apparatus. For
electrospray ionization the apparatus Bruker Microtof ESI-TOF
was used.
General procedure for aziridination
N-(p-Nitrobenzenesulfonyl)-2-(4-methoxybenzyl)aziridine (3m).
To a solution of N-tosylimine (0.2 mmol) in dry THF (10 mL)
cooled to -5 to 0 ◦C under nitrogen atmosphere was added 3 ml
(nearly 5 equivalents) of a diazomethane solution in ethyl ether
prepared according to Vogel’s procedure.24 The reaction was com-
plete in 10–30 min, depending on substrate. The reaction mixture
was concentrated and purified by flash column chromatography
(5% ethyl acetate in hexane as eluent).
=
Oil, obtained in 78% yield. IR(film) nmax: 1321 (S O), 1162
-1
1
=
(S O) cm . H NMR (CDCl3) d: 8.17 (2H, d, J = 8.8, ArH3¢+5¢),
7.88 (2H, d, J = 8.8, ArH2¢+6¢), 6.87 (2H, d, J = 8.6, ArH2+6),
6.59 (2H, d, J = 8.6, ArH3+5), 3.71 (3H, s, OCH3), 3.01-2.90
(2H, m, H2 + H1¢a), 2.88 (1H, d, J = 6.8, H3a), 2.39 (1H, dd,
J=14.2 and 8.2 Hz, H1¢b), 2.30 (1H, d, J = 4.5 Hz, H3b). 13C NMR
(CDCl3) d: 158.5 (ArC4), 150.2 (ArC1¢/4¢), 143.4 (ArC1¢/4¢), 129.6
(ArC2+6), 129.0 (ArC2¢+6¢), 128.7 (ArC1), 123.9 (ArC3¢+5¢), 113.6
(ArC3+5), 55.0 (OCH3), 43.1 (C2), 36.5 (C1¢), 33.5 (C3). MSEI(+)
m/z: 348 [M]+ (26.7), 162 [M-Nz]+ (100), 121 [MeOC6H4CH2]+
(83.9). HRMSEI(+) calcd for C16H16N2O5S [M]+ 348.0780 found
348.0778.
N-(Benzenesulfonyl)-2-(4-bromophenyl) aziridine (2e). Oil, ob-
-1
=
=
tained in 71% yield. IR(film) nmax: 1324 (S O), 1163 (S O) cm .
1H NMR (CDCl3) d: 7.98 (2H, d, J = 7.4 Hz, ArH2¢+6¢), 7,65 (1H,
t, J = 7.2 Hz, ArH4¢), 7,55 (2H, t, J = 7.2 Hz, ArH3¢+5¢), 7.42 (2H,
d, J = 8.0 Hz, ArH3+5), 7.09 (2H, d, J = 8.0 Hz, ArH2+6), 3.75 (1H,
dd, J=7.1 and 4.3 Hz, H2), 3.01 (1H, d, J = 7.1 Hz, H3b), 2.36
(1H, d, J = 4.3 Hz, H3a). MSEI(+) m/z: 338 [M81Br+ H]+ (21.92),
340 [M79Br + H]+ (21.77), 196 [M-Bs]+ (71.2). HRMSEI(+) calcd
for C14H12BrNO2S [M]+ 338.9990 found 338.9985
N-(p-Toluenesulfonyl)-2-(2,4-dimethoxybenzyl)aziridine (3n).
=
Oil, obtained in 74% yield. IR(film) nmax: 1321 (S O), 1162
-1
(S O) cm . 1H NMR (CDCl3) d: 7.66 (2H, d, J = 8.0 Hz,
=
ArH2¢+6¢), 7,19 (2H, d, J = 8.0 Hz, ArH3¢+5¢), 6.82 (1H, d, J =
8.2 Hz, ArH6), 6.32 (1H, d, J = 2.0 Hz, ArH3), 6.24 (1H, dd,
J=8.2 and 2.0 Hz, ArH5), 3.77 (3H, s, OCH3), 3.74 (3H, s, OCH3),
3.03-2.97 (1H, m, H2), 2.78 (1H, dd, J=14.1 and 5.4 Hz, H1¢a),
2.68 (1H, d, J = 6.9 Hz, H3a), 2.54 (1H, dd, J=14.1 and 6.9 Hz,
H1¢b), 2.41 (3H, s, ArCH3), 2.16 (1H, d, J = 4.5 Hz, H3b); 13C
NMR (CDCl3) d: 159.9 (ArC4), 158.1 (ArC2), 144.0 (ArC4¢), 135.1
(ArC1¢), 130.7 (ArC6), 129.4 (ArC3¢+5¢), 127.8 (ArC2¢+6¢), 117.8
(ArC1), 103.9 (ArC5), 98.3 (ArC3), 55.2 (OCH3), 40.5 (C2), 33.3
(C3), 31.8 (C1¢), 21.5 (ArCH3); MSEI(+) m/z: 347 [M]+ (29.1), 192
[M-Ts]+ (100), 151 [(MeO)2C6H4CH2]+ (64.2). HRMSEI calcd for
C18H21NO4S [M]+ 347,1191 found 347,1196.
N -(p-Toluenesulfonyl)-2-(2-bromo-4,5-methylenedioxyphenyl)
aziridine (2v). Oil, obtained in 30% yield. IR(film) nmax: 1321
-1
1
=
=
(S O), 1160 (S O) cm . H NMR (CDCl3) d: 7.88 (2H, d, J =
8.0 Hz, ArH2¢+6¢), 7,35 (2H, d, J = 8.0 Hz, ArH3¢+5¢), 6.94 (1H, s,
ArH3), 6.64 (1H, s, ArH6), 5.93 (2H, s, OCH2O), 3.91 (1H, dd,
J=7.0 and 4.4 Hz, H2), 2.98 (1H, d, J = 7 Hz, H3a), 2.45 (3H, s,
ArCH3), 2.20 (1H, d, J = 4 Hz, H3b). 13C (CDCl3) d: 148.2, 147.5,
144.9, 134.6, 129.8, 129.5, 128.1, 113.9, 112.5, 107.6 (ArC), 101.9
(OCH2O), 41.2 (C2), 35.9 (C3), 21.7 (ArCH3). MSEI(+) m/z: 397
[M81Br]+ (4.34), 395 [M79Br]+ (4.0), 240 [M79Br-Ts]+ (55.6), 161
[M-Ts-Br]+ (100). HRMSEI(+) calcd for C16H14NO4S79Br [M]+
394.9827 found 394.9827.
N-(p-Toluenesulfonyl)-2-(2-methylbenzyl)aziridine (3o). White
N-(p-Toluenesulfonyl)-2-(4-methoxybenzyl)aziridine
(3k).
solid (128–129◦C ethyl acetate–hexane), obtained in 74% yield.
White solid (108–109◦C, ethyl acetate–hexane), obtained in 72%
IR(film) nmax: 1320 (S O), 1159 (S O) cm . H NMR (CDCl3)
d: 7.58 (2H, d, J = 8.0 Hz, ArH2¢+6¢), 7,12 (2H, d, J = 8.0 Hz,
ArH3¢+5¢), 6.99-6.90 (4H, m, ArH), 2.90-2.84 (1H, m, H2), 2.75
(1H, dd, J=14.7 and 5 Hz, H1¢a), 2.65-2.60 (2H, m, H1¢b + H3a),
2.34 (3H, s, ArCH3), 2.12 (3H, s, ArCH3), 2.06 (1H, d, J = 4.4 Hz,
H3b). 13C NMR (CDCl3) d: 144.2, 136.0, 135.2, 134.7, 130.1, 129.4,
129.3, 127.7, 126.6, 125.9 (ArC), 40.4 (C2), 34.4, 32.7 (C1¢/C3),
21.5 (ArCH3), 19.4 (ArCH3). MSEI(+) m/z: 301 [M]+ (9.1), 146
[M - Ts]+ (70.4), 130 [M-TsN-2H]+ (100); HRMSEI calcd for
C17H19NO2S [M]+ 301,11365 obtained 301.1132.
-1
1
=
=
-1
yield. IR(film) nmax: 1321 (S O), 1160 (S O) cm . 1H NMR
(CDCl3) d: 7.67 (2H, d, J = 8.0 Hz, ArH2¢+6¢), 7,21 (2H, d, J =
8.0 Hz, ArH3¢+5¢), 6.95 (2H, d, J = 8.3 Hz, ArH2+6), 6.68 (2H, d,
J = 8.0 Hz, ArH3+5), 3.77 (3H, s, OCH3), 2.94-2.88 (1H, m, H2),
2.77 (1H, dd, J=14.5 and 4.9 Hz, H1¢a), 2.70 (1H, d, J = 6.8 Hz,
H3a), 2.60 (1H, dd, J=14.5 and 7.2 Hz, H1¢b), 2.43 (3H, s, ArCH3),
2.14 (1H, d, J = 4.4 Hz, H3b). 13C NMR (CDCl3) d: 158.3 (ArC4),
144.3 (ArC4¢), 134.8 (ArC1¢), 129.6 (ArC2+6), 129.5 (ArC3¢+5¢), 129.0
(ArC1), 127.8 (ArC2¢+6¢), 113.8 (ArC3+5), 55.1 (OCH3), 41.4 (C2),
=
=
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N-(Benzenesulfonyl)-2-(2-methylbenzyl)aziridine (3p). Oil, ob-
ArH2+5), 5.89 (2H, s, OCH2O), 2.94-2.88 (1H, m, H2), 2.79-2.73
(2H, m, H1¢a+3a), 2.51 (1H, dd, J=14.4 and 7.5 Hz, H1¢b), 2.17 (1H,
d, J = 4.5 Hz, H3b). 13C (CDCl3) d: 147.4 (ArC3/4), 146.3 (ArC3/4),
137.8 (ArC1¢), 133.3, 130.6, 128.8, 127.8, 121.6, 109.1, 108.2 (ArC),
100.8 (OCH2O), 41.6 (C2), 37.1, 32.8 (C3/1¢). MSEI(+) m/z: 317
[M]+ (18.6), 176 [M-Bs]+ (51.7), 77 [C6H5]+ (100). HRMSEI(+)
calcd for C16H15NO4S [M]+ 317.0722. found 317.0725
-1
=
=
tained in 73% yield. IR(film) nmax: 1322 (S O), 1163 (S O) cm .
1H NMR (CDCl3) d: 7.80 (2H, d, J = 7.8 Hz, ArH2¢+6¢), 7.57
(1H, m, ArH4¢), 7,43 (2H, t, J = 7.7 Hz, ArH3¢+5¢), 7.11-7.00 (4H,
m, ArH3+4+5+6), 3.04-2.98 (1H, m, H2), 2.85 (1H, dd, J=14.7 and
5.5 Hz, H1¢a), 2.73 (1H, d, J = 6.7 Hz, H3a), 2.36 (1H, dd, J=14.5
and 4.7 Hz, H1¢b), 2.19 (3H, s, ArCH3), 2.16 (1H, d, J = 4.5 Hz,
H3b). 13C (CDCl3) d: 137.8, 136.0, 135.1, 133.3, 130.2, 129.3,
128.8, 127.6, 126.8, 125.9 (ArC), 40.6 (C2), 34.3, 32.8 (C1¢/C3),
19.4 (ArCH3). MS(EI): 387 [M]+ (3.61), 146 [M+-Bs] (43.9), 132
[M+ - TsN] (79.6), 130 [M+-TsN-2H] (100); HRMSEI calcd for
C16H17NO2S [M]+ 287,0980 obtained 287.10979.
N -(p-Toluenesulfonyl)-2-(Anthracen-9-ylmethylene)aziridine
=
(3u). Oil, obtained in 65% yield. IR(film) nmax: 1321 (S O), 1161
-1
1
=
(S O) cm . H NMR (CDCl3) d: 8.24 (1H, s, ArH10), 8.07-8.05
(2H, m, ArH8+1), 7.93-7.91 (2H, m, ArH4+5), 7.44-742 (4H, m,
ArH2+3+6+7), 7.04 (2H, d, J = 8 Hz, ArH2¢+6¢), 6.50 (2H, d, J =
8 Hz, ArH3¢+5¢), 3.92 (1H, dd, J=15.1 and 3.1 Hz, H1¢a), 3.47 (1H,
dd, J=15.1 and 8.5 Hz, H1¢b), 3.10-3.08 (1H, m, H2), 2.89 (1H,
d, J = 6.8 Hz, H3¢a), 2.42 (1H, d, J = 4.4 Hz, H3¢b), 2.21 (3H, s,
ArCH3). 13C (CDCl3) d: 143.5 (ArC4¢), 133.6 (ArC1¢), 131.3 (ArC9),
129.9 (ArC12+13), 128.8 (ArC4+5), 128.5 (ArC3¢+5¢), 126.9 (ArC2¢+6¢),
126.3 (ArC11+14), 125.8, 124.8 (ArC2/3/6/7), 124.3 (ArC8+1), 41.2 (C2),
32.6, 28.8 (C1¢/3), 21.5 (ArCH3). MSEI(+) m/z: 387 [M]+ (38.4),
210 [M-Anthr.]+ (75.6), 91 [C7H7]+ (100). HRMSEI(+) calcd for
C24H21NO2S [M]+ 387.1293 found 387.1293.
N-(p-Toluenesulfonyl)-2-(2-furanyl)methylaziridine (3q). oil,
=
obtained in 77% yield. IR(film) nmax
:
1322 (S O), 1160
(S O) cm . 1H NMR (CDCl3) d: 7.77 (2H, d, J = 8.1 Hz,
ArH2¢+6¢), 7,30 (2H, d, J = 8.1 Hz, ArH3¢+5¢), 7.18 (1H, s,
FuranylH4), 6.21-6.20 (1H, m, FuranylH3), 6.01 (1H, d, J = 3 Hz,
FuranylH2), 3.04-2.98 (1H, m, H2), 2.80 (2H, d, J = 6 Hz, H1¢),
2.70 (1H, d, J = 7 Hz, H3a), 2.44 (3H, s, ArCH3), 2.17 (1H,
d, J = 4.4 Hz, H3b). 13C (CDCl3) d: 150.7 (FuranylC1), 144.4
(ArC4¢), 141.6 (FuranylC4), 134.9 (ArC1¢), 129.6 (ArC3¢+5¢), 127.9
(ArC2¢+6¢), 110.2 (FuranylC3), 106.7 (FuranylC2), 38.4 (C2), 32.9
(C3), 30.2 (C1¢), 21.5 (ArCH3). MSEI(+) m/z: 278 [M+H]+ (1), 171
[Ts]+ (25.4), 155 [Ts]+ (31.2), 91 [C7H7]+ (100). HRMSEI calcd for
C14H15NaNO3S [M + Na]+ 300.06703 found 300.0664.
-1
=
N-(p-Toluenesulfonyl)-2-(2-bromo-4,5-methylenedioxybenzyl)-
aziridine (3v). Oil, obtained in 50% yield. IR(film) nmax: 1320
-1
(S O), 1160 (S O) cm . 1H NMR (CDCl3) d: 7.65 (2H, d,
J = 8.0 Hz, ArH2¢+6¢), 7,20 (2H, d, J = 8.0 Hz, ArH3¢+5¢), 6.85
(1H, s, ArH3), 6.44 (1H, s, ArH6), 5.93 (1H, s, OCH2O), 5.88
(1H, s, OCH2O), 3.04 (1H, dd, J=14.2 and 4.2 Hz, H1¢a), 2.97-
2.92 (1H, m, H2), 2.78 (1H, d, J = 6.8 Hz, H3a), 2.46 (1H, dd,
J=14.5 and 7.7 Hz, H1¢b), 2.42 (3H, s, ArCH3), 2.20 (1H, d, J =
4.3 Hz, H3b); 13C (CDCl3) d: 147.2, 147.0, 144.2, 134.6, 129.6,
129.4, 127.9, 114.2, 112.4, 110.8 (ArC), 101.5 (OCH2O), 39.9 (C2),
37.4, 32.8 (C3/1¢), 21.5 (ArCH3). MSEI(+) m/z: 411 [M81Br]+ (4.83),
409 [M79Br]+ (4.62), 330 [M-Br]+ (23.6), 175 [M-Ts-Br]+ (67.34),
175 [M-Ts-Br + H]+ (100). HRMSEI(+) calcd for C17H16NO4S81Br
[M]+ 410.9963 found 410.9967.
=
=
N-(p-Toluenesulfonyl)-2-(2-phenylethenyl)aziridine
(3r).
White solid (90–91◦C ethyl acetate–hexane), obtained in
-1
1
=
=
68% yield. IR(film) nmax: 1322 (S O), 1161 (S O) cm . H NMR
(CDCl3) d: 7.80 (2H, d, J = 7.9 Hz, ArH2¢+6¢), 7,28-7.14 (7H,
m, PhH + ArH3¢+5¢), 6.32 (1H, d, J = 15.9 Hz, H3¢), 5.81 (1H,
dt, J=15.9 and 7.5 Hz, H2¢), 2.81-2.78 (1H, m, H2), 2.73 (1H, d,
J = 6.8 Hz, H3), 2.51-2.43 (1H, m, H1¢a), 2.32 (3H, s, ArCH3),
2.22-2.14 (1H, d, H1¢b), 2.17 (1H, d, J = 4.8 Hz, H3b); 13C (CDCl3)
d: 144.5 (ArC4¢), 136.8 (ArC1), 132.6 (C3¢), 129.6 (ArC3¢+5¢), 128.4
(ArC3+5), 128.0 (ArC2¢+6¢), 127.3 (ArC4), 126.1 (ArC2+6), 124.5
(C2¢), 41.3 (C2), 34.6 (C1¢), 32.9 (C3), 21.5 (ArCH3); MSEI(+) m/z:
313 [M]+ (3.1), 222 [M-C7H7]+ (100), 91 [C7H7]+ (97.4). HRMSEI
calcd for C18H19NO2S [M]+ 313.1137 found 313.1133.
Procedure for the in situ homologation–aziridination of 1
To a solution of N-tosylimine (0.36 mmol) in dry THF (10 mL)
cooled to -5 to 0 ◦C under nitrogen atmosphere was added
3 ml (nearly 5 equivalents) of a diazomethane solution in ethyl
ether prepared according to Vogel’s procedure.24 The reaction was
monitored by TLC (30% ethyl acetate in hexane as eluent). Once
the reaction was complete, BF3–etherate (10 mol%) was added and
the reaction allowed to come to room temperature and stirred for
a further 2 h. The reaction mixture was then neutralized with
solid sodium bicarbonate, cooled to 0 ◦C and 3 ml more of
diazomethane was added. The reaction mixture was allowed to
stir for 30 min and then filtered through Celite cake, concentrated
and purified by flash column chromatography (5% ethyl acetate in
hexane).
N -(p-Toluenesulfonyl)-2-(3,4-methylenedioxybenzyl)aziridine
=
(3s). Oil, obtained in 76% yield. IR(film) nmax: 1320 (S O), 1160
-1
(S O) cm . 1H NMR (CDCl3) d: 7.67 (2H, d, J = 8.0 Hz,
=
ArH2¢+6¢), 7,22 (2H, d, J = 8.0 Hz, ArH3¢+5¢), 6.57 (1H, d, J =
8.3 Hz, ArH6), 6.48-6.46 (2H, m, ArH2+5), 5.88 (2H, dd, J =
1.4 Hz, OCH2O), 2.89-2.97 (1H, m, H2), 2.76 (1H, dd, J=14.5 and
4.7 Hz, H1¢a), 2.71 (1H, d, J = 6.8 Hz, H3a), 2.50 (1H, dd, J=14.1
and 7.5 Hz, H1¢b), 2.42 (3H, s, ArCH3), 2.14 (1H, d, J = 4.4 Hz,
H3b); 13C (CDCl3) d: 147.4 (ArC4), 146.2 (ArC3), 144.3 (ArC4¢),
134.7 (ArC1¢), 130.7 (ArC1), 129.4 (ArC3¢+5¢), 127.8 (ArC2¢+6¢),
121.6 (ArC2), 109.1 (ArC5), 108.1 (ArC6), 100.8 (OCH2O), 41.2
(C2), 37.2(C1¢), 32.6 (C3), 21.5 (ArCH3). MSEI(+) m/z: 331 [M]+
(24.3), 176 [M-Ts]+ (100), 91 [C7H7]+ (46.8). HRMSEI calcd for
C17H17NO4S [M]+ 331.0878 found 331.0875.
N-(Benzenesulfonyl)-2-(4-bromobenzyl)aziridine (3e). Oil, ob-
-1
=
=
tained in 25% yield. IR(film) nmax: 1318 (S O), 1160 (S O) cm .
1H NMR (CDCl3) d: 7.74 (2H, d, J = 8.0 Hz, ArH2¢+6¢), 7.61 (1H,
t, J = 7.5 Hz, ArH4¢), 7,41 (2H, t, J = 7.6 Hz, ArH3¢+5¢), 7.20 (2H,
d, J = 8.1 Hz, ArH3+5), 6.87 (2H, d, J = 8.1 Hz, ArH2+6), 2.94-2.84
(2H, m, H1¢+2a), 2.77 (1H, d, J = 6.7 Hz, H3b), 2.48 (1H, dd, J=14
and 8 Hz, H1¢b), 2.19 (1H, d, J = 4.4 Hz, H3a). 13C NMR (CDCl3)
N-(Benzenesulfonyl)-2-(3,4-methylenedioxybenzyl)aziridine (3t).
=
Oil, obtained in 72% yield. IR(film) nmax: 1321 (S O), 1159
-1
(S O) cm . 1H NMR (CDCl3) d: 7.80 (2H, d, J = 7.6 Hz,
=
ArH2¢+6¢), 7,58 (1H, t, J = 7.2 Hz, ArH4¢), 7,44 (2H, t, J = 7.2 Hz,
ArH3¢+5¢), 6.58 (1H, d, J = 7.8 Hz, ArH6), 6.49-6.46 (2H, m,
2972 | Org. Biomol. Chem., 2010, 8, 2968–2974
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d: 137.66, 135.93, 133.35, 131.47, 130.33, 128.92, 127.76, 120.65
(ArC), 41.34 (C2a), 36.83 (C1¢/3a), 32.72 (C1¢/3a). HRMSEI(+) calcd
for C15H14BrNO2S [M]+ 350.9929 found 350.9923.
Prabhakar Raje also thanks PRAXIS program for the award of
research fellowship
Notes and references
N-(Benzenesulfonyl)-2-(4-chlorobenzyl)aziridine (3f). In this
case 50 ml of H2SO4 were used for the rearrangement instead
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=
of BF3. Obtained in 18.3%. IR (film): nmax: 1323 (S O), 1162
-1
(S O) cm . 1H NMR (CDCl3) d: 7.79 (2H, d, J = 7.8 Hz,
=
ArH2¢+6¢), 7.57 (1H, t, J = 7.4 Hz, ArH4¢), 7.44 (2H, t, J = 7.8 Hz,
ArH3¢+5¢), 7.09 (2H, m, ArH4+5), 7.00 (1H, s, ArH2), 6.93 (1H, d, J =
7.2 Hz, ArH6), 2.95 (1H, m, H2a), 2.86 (1H, dd, J=4.6 e 14.4 Hz,
H1¢a), 2.77 (1H, d, J = 6.8, H3a), 2.56 (1H, dd, J=7.6 e 14.4 Hz,
H1¢b), 2.18 (1H, d, J = 4.36 Hz, H3b), 13C-RMN (CDCl3) d: 138.94,
137.63, 134.16, 133.56, 129.70, 128.93, 127.72, 126.97, 126.85
(ArC), 41.01, 37.11, 32.74 (C1¢a+2a+3a). MSEI(+) m/z: 307 [M]+
(8.1), 166 [M-Bs]+ (100). HRMSEI(+) calcd for C15H14ClNO2S
[M]+ 307.0434 found 307.0431.
Procedure for the in situ homologation–aziridination of 2a
To a solution of N-(p-toluenesulfonyl)phenyl aziridine (2a, 0.1 g,
0.366 mmol) in dry THF (10 mL) at room temperature was
added BF3–etherate (10 mol%) and the reaction stirred for 2 h.
The reaction mixture was then neutralized with solid sodium
bicarbonate and cooled to 0 ◦C. To this solution it was added
3 ml (nearly 5 equivalents) of a diazomethane solution in ethyl
ether. The reaction mixture was allowed to stir for 30 min and
then filtered through Celite cake, concentrated and purified by
flash column chromatography (5% ethyl acetate in hexane as
eluent). N-Tosyl-benzylaziridine (3a) was obtained in 33% yield.
Spectroscopic data agree with those from literature.12
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Aziridination of 2-phenyl-N-tosylethanimine (4, X = H)
In a 250 ml round-bottomed flask fitted with a reflux con-
denser and a CaC12 drying tube, a mixture of 2.50 g of p-
toluenesulfonamide (0.0146 mol) and 2.00 g of thionyl chloride
(0.0168 mol) in 40 ml of dry toluene was heated for 5 d at reflux.
After cooling to room temperature, the solvent and excess of SOCl2
were evaporated to leave approximately 3.00 g of dark orange
oil. Kugelrohr distillation gave a total of 1.2 g of N-sulfinyl-p-
toluenesulfonamide (130–140 ◦C, 0.06 Torr) which crystallized
◦
upon standing to a bright yellow solid, mp 47–51 C (lit.25 mp
47–51 ◦C).
To a two-necked 25 mL flask fitted with a syringe cap and
an argon inlet was added 3 mL of dry CH2C12 followed by N-
sulfinyl-p-toluenesulfonamide (0.45 mmol, 98 mg) in 2 mL of
dry CH2C12. The phenyl acetaldehyde (0.3 mmol) was added
via syringe, and the reaction mixture was stirred for 1–2 h at
room temperature. The reaction mixture was kept between 20 and
30 ◦C. After complete conversion of aldehyde (seen by TLC) the
reaction mixture was cooled to 0 ◦C and diazomethane added.
The reaction was monitored by TLC until complete conversion
of the imine. N-Tosyl-benzylaziridine (3a) was obtained in 50%
yield. Spectroscopic data agree with those from literature.12
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Acknowledgements
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We thank Fundac¸a˜o para a Cieˆncia e Tecnologia (Lisbon,
Portugal), PRAXIS program, for partial financial support. Vivek
This journal is
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